The present invention relates to a correction of a variation in colors printed by a printer including a head of inkjet type.
Among printers of the inkjet type, there are printers including multiple nozzles (ink discharge openings) which discharge ink. The respective nozzles discharge dots in multiple sizes (large, middle, and small) according to voltages supplied to the print head. Although a discharge characteristic of the respective nozzle is almost equal, there is a certain level of variation. This variation causes a variation in colors, and there has thus been practiced to correct the variation of the discharge characteristic of the respective nozzles (refer to Patent Document 1 (Japanese Laid-Open Patent Publication (Kokai) No. 2003-182120)). Specifically, the variation of the discharge characteristic of the respective nozzles is corrected based upon errors between ink weights for the large, middle, and small dots and reference values thereof for the respective nozzles.
For example, it is assumed that a reference value of the ink weight for the middle dot is 20 ng, and the actually obtained ink weight for the middle dot is 17 ng. In this case, it is possible to correct this variation by multiplying a recording ratio of the dot corresponding to a tone value by 20/17=1.18.
However, according to prior art as described above, the maximum value of the recording ratio for the middle dot is also multiplied by 1.18. In general, the recording ratios of the large, middle, and small dots are set to equal to or lower than predetermined respective limit values in order to avoid banding and a degradation of granularity. However, if the maximum value of the recording ratio for the middle dot is multiplied by 1.18, the resulting value exceeds the predetermined limit value. The same applied to the large and small dots.
An object of the present invention is to correct a variation in the discharge characteristic among respective nozzles of an inkjet type printer while the recording ratios of dots are equal to or less than predetermined limit values.